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Oil & Gas

Screw Jack Lift the Lid At Houston's New Hydrospace Test Centre

Houston's largest and most advanced hydrostatic test centre was recently opened at Balmoral Group Internationals Rankin Road premises. The test centre has a wide variety of pressure vessels, ranging from 800mm diameter x 2200mm long, all the way up to 2500mm diameter x 8500mm long. This fully comprehensive facility carries out simultaneous fully instrumented pressure and water ingress tests to pressure ratings up to 5000psi SWP.

The largest pressure vessel rated at 5000psi SWP, weighs in at 138 tons with a 35-ton lid. The body is sunk into the test centre floor and the lid has to be removable for maintenance and installation of test products in the vessel.

In order to remove the pressure vessel lid it is raised 1045mm and moved 6m to the side where it is lowered onto a rest while the test pieces are installed. The procedure is reversed to replace the lid. To achieve suitable operation times the lid is required to be lifted at 95mm/min and traversed at 2.4m/min.

To source the lid lifting and traversing mechanism, Balmoral Group approached Screw Jack to design and supply the complete vehicle and control system.

The design, manufacture and testing of the vehicle were completed at Screw Jack’ factory in Fraserburgh, Scotland. Three teams of engineers worked on the project utilising some of the latest computer aided engineering software to aid system design and project co-ordination.

The vehicle consists of a gantry type framework mounted on four two-wheel units located in each corner. One wheel unit on each side is driven to provide the linear motion to translate the lid to and from the vessel. A four-actuator system on top of the framework is designed to lift and lower the lid on and off the vessel. The control system for the vehicle is mounted on one side of the framework and travels with the vehicle, with a remote operator console located beside the pressure vessel.

As the vehicle had to be built, tested, dismantled for shipping then re-built in Houston, the framework was designed in two sections, each section of the frame representing one side of the vehicle. The sections bolted together on two main flanges at each end of the vehicle. The frame was then located onto four wheel-assemblies, each consisting of two wheels mounted on support bearings in a self-contained structure. This assembly was bolted to the framework for initial location and welded in place for final positioning. Each of the wheel assemblies had different modular wheel options. One side of the vehicle wheels had guiding flanges that located in a steel channel in the floor to ensure vehicle location. The two front pairs of wheel units had drive sprockets that attached to a motorised reduction gearbox mounted on the framework. As it was not possible to mechanically link the two motorised gearboxes for the vehicle drive, they were electronically synchronised.

The actuator system designed to lift the lid consisted of four actuators mechanically linked in a "U" configuration with a main drive unit at one end. The actuators were special units based on Screw Jack 300kN Metric machine screw model. They were of the inverted type incorporating wear monitoring for the gear sets. The specially designed lifting screws had conical locating ends so that when the lid was lifted to its full height the screws were locked in the framework, thus preventing the lid swaying when it was translated to and from the vessel. A motorised reduction gearbox with bevel gearboxes to direct the drive line provided drive to each of the four actuators. The motor unit included an integral brake for secure load holding while parked. For positioning purposes a rotary cam limit switch was connected to the actuator system, providing emergency over-travel limits and normal system stop limits. The actuator system has two mechanical safety features. 1), It is self-locking and therefore will not back-drive, even in the remote chance of brake failure on the motor. 2), The wear monitors on each actuator provide warning of gear wear and provide a safe working indication that an actuator requires refurbishment. The actuator systems motion was controlled the main control system.

The main control system consisted of two parts, the vehicle drive and the actuator drive. All three sections of the control system were based on advanced inverter controls. The vehicle drive consisted of two inverters with integral motion control cards linked together to provide precise synchronised speed and position movement for both vehicle motors. An encoder on each of the motors provided feedback. Having an integral motion control card in the inverters eliminated the need for extra control items such as PLC's and reduced the systems installation space. The motion control program enabled the vehicle to move from a home position to a target position, which was set via an HMI on the main panel. This position was set as the vessel position and was variable for commissioning purposes. The actuator drive provided variable speed settings for the lid lift while maintaining full torque capability.

The main panel had a set of operator controls and HMI interfaces. However, as this would be moving during operation, an additional remote operator console located the side of the pressure vessel was also provided. Both the vehicle and actuator drive systems could be operated in automatic and jog modes. For safety reasons several emergency stop units are mounted at readily accessible points around the vehicle.

Before being shipped to Houston the complete vehicle system was load-tested at Screw Jack. In order to test the vehicle Screw Jack built a simulated arrangement of the pressure vessel installation and attached 50 tonne of test weights. The vehicle successfully passed its factory commissioning tests first time, an achievement that was repeated in Houston when the vehicle was re-built.

The vehicle provides a flexible and compact automated system for removing and fitting the pressure vessel lid.